Nanostructure having metal nanoparticles and a method of assembly thereof

ABSTRACT

A nanostructure and method for assembly thereof are disclosed. The nanostructure includes a gain medium nanoparticle; an output coupler nanoparticle being discrete from and linked to the gain medium nanoparticle; and a plurality of metal nanoparticles being linked about the gain medium nanoparticle, wherein the gain medium nanoparticle and the output coupler nanoparticle are included in the nanostructure in a one to one ratio.

CROSS-REFERENCE TO RELATED APPLICATION

This Application is a Divisional of U.S. application Ser. No. 13/959,130filed Aug. 5, 2013 which is a Continuation-In-Part of co-pending U.S.application Ser. No. 12/379,930 filed Mar. 4, 2009, the contents ofwhich are incorporated herein by reference.

FIELD

The present application relates to nanostructures. More particularly,the application relates to metal nanoparticles and methods of assemblingnanostructures including metal nanoparticles.

BACKGROUND

Gold metal nanoparticles have been used as a pigment to, for example,stain glass. More recently, there has been research into developingmetal nanostructure assemblies, including structures made from noblemetals such as gold and silver. For example, it is known to use anelectromagnetic wave to excite a strong resonance condition in metalnanoparticle assemblies, which can lead to enhanced, localizedelectromagnetic fields.

SUMMARY

A nanostructure is disclosed which includes a gain medium nanoparticle;an output coupler nanoparticle being discrete from and linked to thegain medium nanoparticle; and a plurality of metal nanoparticles beinglinked about the gain medium nanoparticle, wherein the gain mediumnanoparticle and the output coupler nanoparticle are included in thenanostructure in a one to one ratio.

An exemplary method is also disclosed for assembling an exemplarynanostructure. The method includes attaching a first linker to a gainmedium nanoparticle; attaching the first linker to a substrate largerthan the gain medium nanoparticle; attaching a plurality of secondlinkers to the gain medium nanoparticle; detaching the first linkerconnected to the gain medium nanoparticle from the substrate; attachinga plurality of third linkers to an output coupler nanoparticle;attaching the first linker to one of the plurality of third linkers;attaching a plurality of fourth linkers to a plurality of metalnanoparticles; and attaching each of the plurality of second linkers toeach of the plurality of fourth linkers.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention thattogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a diagram of an exemplary nanostructure including a singletier of metal nanoparticles.

FIG. 2 is a diagram of an exemplary nanostructure including two tiers ofmetal nanoparticles.

FIG. 3 shows graphs depicting exemplary intensity enhancement and metalnon-radiative lifetimes in relation to wavelength for single tier andmulti-tier nanostructures.

FIG. 4 shows graphs depicting effects of different types of dielectricson a resonance wavelength of a nanostructure with respect to intensityenhancement and metal non-radiative lifetimes.

FIGS. 5A-D show exemplary linker types used to assemble nanostructures.

FIGS. 6A and 6B are high level diagrams showing an exemplary gain mediumnanoparticle and an exemplary first linker temporarily connecting to alarger substrate.

FIGS. 7A and 7B are high level diagrams showing an exemplary method ofconnecting a gain medium nanoparticle and an output couplernanoparticle.

FIGS. 8A and 8B are high level diagrams showing an exemplary method ofconnecting a gain medium nanoparticle and a tier of metal nanoparticles.

FIG. 9 is a high level diagram of an exemplary injection structure.

FIG. 10 is a diagram of an exemplary nanostructure anchored to asubstrate.

DETAILED DESCRIPTION

FIG. 1 is a diagram of an exemplary nanostructure 100. The nanostructure100 includes a gain medium nanoparticle 110, and an output couplernanoparticle 130, at a one to one ratio, linked about the gain mediumnanoparticle. A plurality of metal nanoparticles 120 a to 120 e islinked about the gain medium nanoparticle.

A spherical metal nanoparticle in free space can act as a resonator witha frequency peak at the wavelength where the real part of the dielectricconstant is negative. The resonant electromagnetic behavior is a resultof confinement of conduction electrons to the small metal nanoparticlevolume, where dimensions are much smaller than a wavelength of anexcitation electromagnetic wave. This is sometimes called the plasmonicresonance. The plasmonic resonance condition may be a function of adielectric constant of the environment surrounding the nanostructuresand can cause high local field intensities. By arranging multiplenanoparticles in certain geometries that tend to focus the field, largelocalized field enhancements can be provided. When a nanoparticlearrangement creates a resonance cavity, it can have the effect ofincreasing the system Q beyond that of individual nanoparticles.

Embodiments of a nanostructure include at least one metal nanoparticletier that can confine approaching light in almost any direction andexcite surface plasmons. These plasmons, in turn, can produce a focusedelectric field (i.e., electromagnetic enhancement) in a resonance cavityhaving the at least one tier of metal nanoparticles.

In the exemplary nanostructure 100 of FIG. 1, a first metal nanoparticletier 120 includes the metal nanoparticles 120 a to 120 e and the outputcoupler nanoparticle 130. Each metal nanoparticle 120 a to 120 e of thefirst tier may be linked about the gain medium nanoparticle 110 (e.g.,attached to the gain medium nanoparticle). The output couplernanoparticle 130 may also be linked to the gain medium nanoparticle 110in a one to one ratio.

The tier 120 of metal nanoparticles 120 a to 120 e shown in FIG. 1 canact as a three-dimensional feedback structure or resonance cavity thatamplifies the electric field within the resonance cavity via theelectromagnetic enhancement. The enhanced field can be highly localizedat a place serving as a “hot spot” of field enhancement and a site forlocating a material desired to be subject to the enhanced field, such asthe gain medium nanoparticle 110.

Metal nanoparticles 120 a to 120 e can be, for example, any kind ofmetal nanoparticle assembly that has a dielectric constant having anegative real part. Examples of metal nanoparticles for the metalnanoparticle assemblies may include gold, silver, aluminum, copper,titanium, chromium, and other metals capable of supporting surfaceplasmons. The metal nanoparticles 120 a to 120 e can be on the order of15 nanometers, for example, although larger or smaller nanoparticles maybe used to construct the nanostructure 100. Metal nanoparticlescurrently are available in a number of different types and sizes from acommercial source, such as Sigma Aldrich™ or Ted Pella, Inc., or theycan be prepared using known methods. For example, a colloidal formationmethod of preparing metal nanoparticles is described by B. V, Enüstün etal. in “Coagulation of Colloidal Gold” (J. Am. Chem. Soc., 85, 3317(1963)).

In FIG. 1, the exemplary nanostructure 100 has a somewhat centrallylocated nanoparticle 110. This nanoparticle serves as a gain medium forthe nanostructure, capable of producing a stimulated emission of energy.The gain medium nanoparticle 110 can comprise a photocatalytic materialthat is capable of generating electrons and holes, or electron-holepairs such as excitons, which may combine to generate photons. Thismaterial may be a semiconductor material or any other desired materialto be exposed to an enhanced field. For example, gain mediumnanoparticle 110 may be a light-emitting semiconductor material, such asII-VI or III-V semiconductor material, for example CdSe, GaAs, InSb, orLiNbO₃, or other types of semiconductor materials. A semiconductornanoparticle can replicate the characteristics of bulk semiconductors ona scale of a few nm (e.g. 1-100 nm), and is sometimes referred to hereinas a quantum dot or a nanocrystal. Semiconductor nanoparticles areavailable in a variety of types, sizes, and shapes.

While embodiments are described herein including a photocatalyticmaterial as a gain medium material nanoparticle 100, it is to beunderstood that the gain medium can comprise another kind of material,such as a dielectric material. For example, the gain medium can includenonlinear BZN dielectric ceramics or other linear or nonlineardielectric material. For example, embodiments using nonlinear materialas the gain medium can enable high speed electro-optical interactioncapabilities. For instance, the field enhancement mechanism can act onthe nonlinear material to give it a much higher effectivelynonlinearity. This can enable devices such as high speed electro-opticalswitches, routers, and wavelength converters with a very small formfactor. Additionally, embodiments may use field tunable nonlineardielectric material (e.g., BZN) to control the enhancement strength andpeak wavelength.

Embodiments can include a magnetic nanoparticle material, such as fineferromagnetic particles of iron ferrite, or other kinds of material thatare responsive to a magnetic field, as the gain medium to which thefirst tier 120 of metal nanoparticles 120 a to 120 e is attached.

Embodiments can include a nanoparticle that does not need to interactwith the surrounding feedback structure and which can even be removed,if desired. For example, a “placeholder” nanoparticle may be provided tobuild a metal nanoparticle assembly and thereafter removed. The size ofsuch a placeholder nanoparticle may be of the order of 1 nm, forexample, although a placeholder nanoparticle can be larger or smallerthan 1 nm.

The gain medium nanoparticle 110 also can be a semiconductornanoparticle covered with a shell layer of another material, such as awider bandgap semiconductor material to form a core-shellheterostructure. A heterostructure can affect (e.g., minimize) thenumber of surface traps, yield greater charge recombination (quantumyield), reduce leakage current, and improve injection characteristics.An exemplary heterostructure may be synthesized with less than fivepercent wavelength polydispersity (e.g., see T. Kippeny, “ExcitonDynamics in Cadmium Selenide/Zinc Selenide Core/Core-Shell Nanocrystalsas Effected by Surface Ligands Modification Using FemtosecondFluorescence Upconversion”).

For example, a CdSe semiconductor nanoparticle can serve as the core anda ZnS epitaxial layer can function as the shell, although othersemiconductor material types may be used to form the heterostructure.The zinc sulfide shell can be applied by making a reaction solution of50/50 molar of 0.5 M zinc naphthenate mixed with 8 M sulfur indibutylether (DBE) diluted to 0.5 M with toluene. This reaction solutioncan then be heated to 200° C., and added dropwise to the CdSe corenanoparticles. As shell growth proceeds (e.g., as reagent solution isadded dropwise), the emission increases until maximum amplitude isobserved. The emission peak blue-shifts slightly and then red-shifts asreagent addition is continued. Addition of shelling reagent is haltedwhen the emission peak red-shifts to the original core emissionwavelength. This results in between 6 to 8 monolayers of ZnS shell foreach core-shell nanoparticle heterostructure.

The output coupler nanoparticle 130 can be used for directing anemission from the nanostructure 100 produced by the gain mediumnanoparticle 110. The output coupler nanoparticle can also be used as ananchor for linking the nanostructure 100 to a substrate. The outputcoupler nanoparticle 130 can take the place of a traditional outputcoupler, which typically would be a semitransparent dielectric, (e.g., amirror used in a laser resonator). The output coupler nanoparticle 130can enable photons to be ejected collinearly by providing a mechanismfor the nanostructure to he directionally aligned as well as a way inwhich the photons may be outputted. The output coupler should occur at aone to one ratio with the gain medium nanoparticle.

The output coupler nanoparticle 130 can comprise a material such assilicon dioxide, for example, or any other type of material which canserve as a “defect” in the resonance cavity that directs the emission ofexcitons produced by the gain medium nanoparticle 110. For example,output coupler 130 can comprise silicon carbide (SiC), silicon (Si) orgermanium (Ge) for wavelengths in the infrared range, or sapphire forwavelengths in the visible light range. Synthesis of silicon dioxidenanoparticles is known and can be accomplished by hydrolyzingtetraethylortho-silicate (TEOS) in water, ammonia, and ethanol. Forexample, varying the water/TEOS ratio, the concentration of ammonia, thefeed rate of the reactant, and the temperature, silica nanoparticles canbe provided that range in size from 10 to 350 nanometers (e.g., see S.K. Park, et al., “Preparation of silica nanoparticles: determination ofthe optimal synthesis conditions for small and uniform particles”).

Referring to FIG. 1, the gain medium nanoparticle 110, the metalnanoparticles 120 a to 120 f, and the output coupler nanoparticle 130can be linked using organic linkers. A first linker 121, a second linker122, and a connection point 123 between the first and second linkers,are provided between the gain medium nanoparticle 110 and each metalnanoparticle of tier 120. A third linker 131, a fourth linker 132, and aconnection point 133 between the third and fourth linkers are providedbetween the gain medium nanoparticle 110 and the output couplernanoparticle 130. The linkers connecting the gain medium nanoparticle110, the tier of metal nanoparticles 120, and the output couplernanoparticle 130 can be any organic ligand type, such as alkane linkersor polyethylene glycol (PEG) linkers, or another type of linkercomprised of organic material.

FIG. 2 is a diagram of an exemplary nanostructure 200 with a first tier220 of metal nanoparticles 220 a to 220 e arranged about a gain mediumnanoparticle 210 and a second tier 240 of metal nanoparticles 240 a to240 e arranged about the first tier 220. By varying the number of tiersof metal nanoparticles, the relative sizes of the metal nanoparticles,and/or the distances between the metal nanoparticles, parameter valuescan be determined, which allow for extraction of a maximum enhancementfrom a given nanoparticle configuration.

An exemplary nanostructure embodiment can include a metal nanoparticleand/or gain medium nanoparticle shape chosen to tune the structure to aparticular resonant wavelength. For example, although the nanoparticlesshown in FIG. 1 and FIG. 2 are depicted as spheres, the shape of thenanoparticle can be a rod, triangle, plate, pentagon, ellipsoid, or anyother desired shape. Other parameters that may be controlled to increaseelectromagnetic field enhancement include varying the size of a metalnanoparticle and varying the size of metal nanoparticles from one tiergroup relative to another.

Keeping the distances between the nanoparticles proportional whileincreasing only the sizes of the nanoparticles can yield a high gainincrease that follows a power law with the sizes of the nanoparticles.The non-radiative decay rate does not necessarily increasecorrespondingly. By bringing the nanoparticles closer together for agiven nanoparticle diameter set, the enhancement and non-radiativelifetime can, for example, increase exponentially.

The associated wavelength of a gain medium nanoparticle, for example, asemiconductor nanoparticle may be adjusted by, for example, controllinga size (e.g., diameter) or shape of a nanoparticle to tune it to adesired emission or lasing wavelength. For example, a range ofwavelengths from 490-620 nm, or lesser or greater, can be achieved forCdSe semiconductor nanocrystals by appropriately varying the diameter ofthe CdSe nanoparticle. Wider or narrower ranges of wavelengths can beachieved by using other semiconductor material compositions.

While FIG. 1 shows nanostructure 100 as having metal nanoparticles 120 ato 120 f attached to six “sides” of a gain medium nanoparticle 110, withthree orthogonal axes, other embodiments may be arranged on fewer ormore axes and utilize a fewer or greater number of metal nanoparticlesper nanostructure to focus the field. There may also be a fewer orgreater number of nanoparticles per tier. The pattern of the overallnanostructures may be self-similar or any other type of pattern.Embodiments can be configured to include more than one tier of metalnanoparticles to amplify (e.g., increase or decrease (i.e., attenuate))the electric field within the cavity. There should still exist however,the ratio of one to one between the gain medium nanoparticle 110, andthe output coupler 130. Furthermore, some embodiments of nanostructuregeometries may include two or more tiers to provide large localizedfield enhancements. In FIG. 2, a distance d1 between, a metalnanoparticle in tier 220 and the gain medium nanoparticle 210, and adistance d2 between a metal nanoparticle in tier 240 and a metalnanoparticle of tier 220 can be set to particular values to controlfield enhancement. Because the nanostructures 100 or 200 can beassembled to be smaller than the wavelength of light, for example, insizes on the order of about 100-200 nm, these nanostructures can have avery high packing density that permit their use in a variety of opticalapplications.

FIG. 3 describes graphs showing increased enhancement provided byexemplary single tiered and multi-tiered structures. As shown in FIG. 3,the graph 310 represents enhancement provided by a nanostructure havingonly one tier including two metal nanoparticles around a centrallylocated nanoparticle, and the graph 320 represents enhancement providedby adding a second tier of metal nanoparticles spaced from, and about afirst tier of metal nanoparticles. The second tier provides twoadditional metal nanoparticles, resulting in a nanostructure with atotal of four metal nanoparticles around a centrally locatednanoparticle. As can be seen from graph 310, the exemplary nanostructurehaving only a single metal nanoparticle tier can provide a slightenhancement to the field and has an enhancement peak at about 525 nm.Providing additional metal nanoparticle tiers can increase enhancementintensity. For example, graph 320 shows a substantial increase inenhancement intensity around 530 nm in a nanostructure provided with asecond metal nanoparticle tier located a distance farther from the firstmetal nanoparticle tier.

FIG. 3 also includes a graph 330, which represents a metal non-radiativelifetime (i.e., the 8rate at which the gain medium nanoparticle couplesto the non-radiative modes of the metal nanoparticles) resulting fromeither the one-tier structure corresponding to graph 310 or the two-tierstructure corresponding to graph 320. Graph 330 demonstrates anegligible increase in the metal non-radiative lifetime (i.e., the graphof the metal non-radiative lifetime for the one tier structure coincidesor overlaps with the graph of the metal non-radiative lifetime for thetwo tier structure) when a second metal nanoparticle tier is provided toa nanostructure according to embodiments. Hence, the addition of metalnanoparticle tiers can not only increase enhancement intensity, but alsocan do so with no substantial increase of coupling to the non-radiativelifetime. That is, a significant increase in enhancement can be obtainedalmost independently of non-radiative loss by optimizing the geometry ofthe system.

Embodiments can optionally include embedding the nanostructure in apolymer or other type of material that would provide support to thenanostructure. Additionally, this would permit another aspect of tuningbecause the frequency and intensity of the plasmonic resonance issensitive to the dielectric properties of the surrounding medium. Forexample, the plasmonic resonance can be sensitive to a refractive indexof matter close to the nanostructure surface.

FIG. 4 demonstrates the effects a dielectric constant can have on thefield enhancement of an exemplary nanostructure and corresponding metalnon-radiative lifetime. In FIG. 4, graphs 410, 420, and 430 showenhancements in the structure for surrounding environments of air,glass, and water, respectively. As shown, an increase in the dielectricconstant of a material surrounding the nanostructure causes acorresponding increase in the field intensity enhancement and ared-shift of the peak wavelength.

Graphs 411, 421, and 431 of FIG. 4 show the metal non-radiative lifetimecorresponding to the non-radiative recombination rate for air, glass,and water, respectively. These graphs demonstrate that the non-radiativelifetime decreases as the dielectric constant of the surroundingmaterial increases. Comparing graphs 410 and 420 with graphs 411 and421, it can be seen that as the enhancement increases by an order ofmagnitude between air and glass, the non-radiative decay rate decreasesby a factor of about 2. As enhancement grows, the gain mediumnanoparticle non-radiative recombination rate into the metal grows aswell, but at a rate much smaller than the enhancement growth rate, thusmaking dielectric shifting an efficient enhancement tuning method.Hence, a dielectric material not only can provide support for ananostructure, it can also provide a way to fine-tune the enhancementstrength and peak wave length of a nanostructure.

Another optional enhancement control variable is the inclusion of acoating on the metal nanoparticles that has a different dielectricconstant than the metal. For instance, it is possible to tune theenhancement and/or the resonance wavelength of the nanostructure bychanging the surrounding coating material and its correspondingdielectric constant. For example, silica may be provided as a metalnanoparticle coating between 2-4 nanometers thick, although this coatingmay be have a lesser or greater thickness. The growth of the silicashell as a coating is known, and can be controlled, for example, by themethod described by L. M. Liz-Marzán, et al. in “Synthesis of NanosizedGold-Silica Core-Shell Particles” (Langmuir, 12, 4329 (1996)).

Embodiments can include a nanoparticle having non-linear opticalproperties placed in a location of focused electromagnetic field (i.e.,an enhanced field location). This field can act on the nonlinearmaterial, potentially yielding a much higher effective nonlinearity.Such nanoparticle materials may exhibit second or third ordernon-linearity, and can change the optical properties of these materialsas a function of a field in which they are placed. For example, using anon-linear material for the gain medium nanoparticle would permit opticbehavior that would normally occur at a high intensity to occur at lowerintensity (e.g., an order of magnitude lower). This can substantiallyincrease the potential applications for such a structure, such as moreefficient optical switching applications.

A self-assembly method for creating this nanostructure can permitcontrol to be retained over the number of layers, particle materialcomposition, size, shape and/or overall development of thenanostructure. This method can permit the structure to have aself-guided assembly that yields a high volume of product due to theselective nature of self-assembly chemistry (i.e. because each particlecan selectively bind to another kind of particle, there can be a highyield of the desired product).

An exemplary method for assembling a nanostructure includes attaching afirst linker to a gain medium nanoparticle, and attaching the firstlinker to a substrate larger than the gain medium nanoparticle. Aplurality of second linkers is attached to the gain medium nanoparticle.The first linker connected to the gain medium nanoparticle is detachedfrom the substrate. A plurality of third linkers is attached to anoutput coupler nanoparticle. The first linker is attached to one of theplurality of third linkers. A plurality of fourth linkers is attached toa plurality of metal nanoparticles. Each of the plurality of secondlinkers is attached to each of the plurality of fourth linkers.

Embodiments can be carried out by using organic linkers that attach toanother kind of linkers but not to themselves. For example, differentkinds of organic linkers can be used to assemble the exemplarynanostructure. The terminal groups of the linkers can be, for example, athiol group for the gain medium nanoparticle binding, a silyl group forthe output coupler nanoparticle binding or a carboxyl group for themetal nanoparticle binding. The terminal groups of the linkers can bedesigned for peptide binding as a mechanism for the overall assembly ofexemplary nanostructures. Peptide bonding can occur when a carboxylgroup of one molecule reacts with the amino group of another molecule ina condensation reaction.

FIG. 5A to 5D show four exemplary linkers that can be used for thenanostructure chemical self-assembly. These linkers can act analogouslyto magnets. Just as magnets have two distinct poles which only connectnorth to south, but not north to north or south to south, the linkerscan attach at certain ends, and not others, and use these attachmentpoints to connect nanoparticles.

FIG. 5A shows an amino-silane linker which has an amine (NH₂) terminalgroup at one end and a trimethoxysilane (Si(OCH₃)₃) terminal group atthe other end. FIG. 5B shows a silyl-carboxylic acid linker which has atrimethoxysilane terminal group at one end and a carboxylic acid (COOH)terminal group at the other end. FIG. 5C shows a carboxy-thiol linkerwhich has a carboxylic acid terminal group at one end and a thiol (SH)group at the other end. The linker in FIG. 5D is anN-9-fluorenylmethoxymcarbonyl (Fmoc)-protected amino-thiol linker, whichincludes an Fmoc protecting group covering the amine terminal group.These are exemplary linkers for an exemplary self-assembly method,however, this method is not limited to using these types of linkers forassembling a nanostructure.

The four linkers can be chemically similar, providing a comprehensivesynthesis plan for creating linkers that minimizes the total number ofrequired precursors. Each of the four linkers can be created by startingwith two chemical precursors. Various other precursors (e.g. adicarboxylic acid or a carboxylic acid-alcohol) can be inserted into theprocess. For example, a C₂₀ dithiol can be used as a precursor ratherthan starting from a C₂₀ diol. Exemplary conversions that can be carriedout during synthesis include: alcohol to thiol, carboxylic acid, primaryamine, or alkene; and alkene to trimethoxysilane.

To ensure that the nanostructure is self-assembled efficiently andconsistently, the linker attachments can be controlled by creating aprotected surface on the gain medium nanoparticle. This can beaccomplished by temporarily attaching the nanoparticle to a temporaryhost such as a polystyrene bead (PSB) or other neutral substrate.Another aspect of control can be achieved by using linkers with twodifferent terminal functional groups, which form attachments to certainother terminal functional groups, but not others. These various linkerscan be assembled with two kinds of exemplary chemical precursors. Inaddition, protection from protecting groups such as, for example,pyridine can be carried out to minimize expensive product loss.Tetrahydropyran (THP) can be used as the protecting group for thealcohol in light of its stability toward most chemical groups,especially nucleophiles. The following sections will describe in detailexamples for the synthesis and characterization of the temporary host,precursors, and bi-functional linkers required to build thenanostructure.

Hydroxyl-PSB Synthetic Modification

An exemplary method for attaching a linker to the temporary host surfacefor binding to the gain medium nanoparticle can proceed as follows. Dryresin is added to an oven-dried flask, washed, and pre-swelled with dry,O₂ free dimethylformamide. The linker is added in 5-molar equivalentsexcess and allowed to dissolve. Dichlorobenzoyl chloride (DBC) can thenbe added in 8-fold excess and the mixture is agitated for 18 hours. Themodified resin is then washed, allowed to dry, and stored oxygen free.

Precursor A

1,12 Dodecanediol (100 ml, 0.57 mol) can be added to two molarequivalents of red phosphorus and 6 molar equivalents of iodine. Thismixture is then heated to 130° C. and allowed to stir for 8-10 hours.After being decanted from unused solids, the diiodoalkane is thendissolved in dry dichloromethane (DCM) along with a 1.1 molar excess ofsodium hydrogen sulfide and heated for 4 hours at reflux. After beingdecanted from unused solids, the DCM is removed via rotary evaporation.The disulfide can then be confirmed by ¹H and ¹³C NMR.

To protect one end of the disulfide, tetrahydropyran (THP) is added inequal molar concentration along with catalytic acid in DCM and stirredat 35° C. overnight. The resulting mixture may then be chromatographedon silica. Dichloromethane can be used to wash the unbound di-THP whileswitching to acetone can remove the desired mono protected dithiol. 2molar equivalents of red phosphorus and 6 molar equivalents of iodineare then added while heating the solution to 130° C. The reaction isstirred for 8-10 hours and then decanted. The iodated intermediateproduct, or precursor A, can be confirmed with ¹H and ¹³C NMR and GCMS.

Precursor B

1,12 Dodecanediol (100 ml, 0.57 mol) can be added to an equal molarequivalent of THP along with catalytic acid in DCM and stirred at 35° C.overnight. The resulting mixture can then be chromatographed on silica.Dichloromethane can be used to wash the unbound di-THP from the column,while the addition of acetone can remove the desired mono-protectedalcohol. The unprotected diol can then remain on the column. Solvent maybe removed by rotary evaporation. The required intermediate product canbe confirmed with ¹H and ¹³C NMR and GCMS. The mono-protected diol canthen be added to two molar equivalents of red phosphorus and 6 molarequivalents of iodine. This mixture is then heated to 130° C. andstirred for 8-10 hours. After decanting and filtering from unused solidreactants, the mono-protected alcohol ω-iodide, or precursor B, may beconfirmed with ¹H and ¹³C NMR and GCMS.

Ligand 1 Synthesis

Precursor B (0.1 mol) can be dissolved in ethanol and sparged with dryammonia gas at 5 psi while stirring for 4-6 hours. The resulting aminohalide salt is quenched with alcoholic potassium hydroxide. Acid canthen be added to neutralize the solution, in slight excess fordeprotection of the THF-alcohol. After decanting and filtration, theproduct is isolated via rotary evaporation. Two molar equivalents of redphosphorus and 6 molar equivalents of iodine are then added to thealcohol intermediate. This mixture is then heated to 130° C. and allowedto stir for 8-10 hours. After decanting and filtering from unused solidreactants, the mono-protected alcohol ω-amine will be treated withalcoholic potassium hydroxide. The resulting solution will be decantedand filtered for unused reactants, and the solvent can then be removedby rotary evaporation. The resultant intermediate may be dissolved indry DCM and dried over magnesium sulfate. Once filtered, HSi(OCH₃)₃)will be added in enough excess to ensure total dryness. The product canbe confirmed with ¹H and ^(—)C NMR, GCMS, and FT-IR.

Ligand 2 Synthesis

Precursor B (0.1 mol) can be solvated in ethanol and the resultantsolution saturated with potassium hydroxide and stirred overnight.Solids are removed from the resulting solution by decanting/filtrationand solvent removed by rotary evaporation. The intermediate product isthen dissolved in dry hexanes and one equivalent of trimethoxysilane isadded. Catalytic aqueous HCl is then added for deprotection of thealcohol. Silver carbonate in four molar excess can then be directlyadded and the solution is refluxed for 24 hours. Silver(I) oxide formedin situ by the addition of silver nitrate in excess sodium hydroxide canbe added and then refluxed for a further 24 hours. After decanting andfiltering from unused solid reactants, the ω-carboxyl methoxysilane canbe re-crystallized from acetone/hexanes. Product may be confirmed with¹H and ¹³C NMR, GCMS, and FT-IR.

Ligand 3 Synthesis

Precursor A (0.1 mol) can be added to saturated alcoholic potassiumhydroxide and vigorously vortexed for eight hours. Upon reactioncompletion, any solids can be filtered from the solution and solvent canbe removed by rotary evaporation. The remaining product material canthen be dissolved in 50/50 hexanes/benzene along with a four molarexcess of silver carbonate on cellulite (Fétizon's reagent) and broughtto reflux overnight. Solids are removed by filtration. Silver(I) oxideformed in situ by the addition of silver nitrate in excess sodiumhydroxide and refluxed for a further 24 hours. When the silver(I) oxideis fully formed, the basic solution can be made acidic to facilitateremoval of the tetrahydropyran (THP) protecting group. Excess sodiumbicarbonate can be added to neutralize the solution. Afterdecanting/filtration, the product can be isolated by rotary evaporationand can be characterized with ¹H and ^(—)C NMR, GCMS, and FT-IR.

Alternate synthesis from hydroxyl carboxylic acid is available in C₁₀,C₁₂, and C₁₆ chain lengths. Protection of the acid moiety can beaccomplished via an oxazoline. The alcohol can then be converted to athiol in two steps via PI₃/Na⁺SH⁻ as discussed above.

Ligand 4 Synthesis

Precursor A (0.1 mol) can be solvated in ethanol or a 50/50 mixture ofmethanol/dichloromethane (DCM) and then sparged with dry ammonia gas at5 psi. The vessel can then be stirred for 4 to 6 hours. The resultingamino halide salt can be quenched with alcoholic potassium hydroxide.Acid can then added to neutralize the solution, with slight excess fordeprotection of the thiol. The solution can then be filtered to removeany solids and isolated by rotary evaporation. The intermediate productcan then be redissolved in DCM and mixed with excessFmoc-hydroxysuccinimide. The resulting product can then berecrystallized from acetone/hexanes. The pure product can be confirmedwith ¹H and ^(—)C NMR, GCMS, and FT-IR.

Overall Nanostructure Synthesis

A gain medium nanoparticle can be stabilized by protecting grouplinkers. For example, the core-shell nanoparticles synthesized asdescribed above in paragraph 0020 can be stabilized by, for example,trioctylphosphine oxide (TOPO) and hexadecylamine (HAD) ligands. TheseTOPO/HDA ligands can be ligand-exchanged with the organic linker ligandsto permit assembly of the nanostructure. Initially, the TOPO/HDA ligandscan be exchanged for pyridine. The pyridine-stabilized core-shellnanoparticles can then be precipitated with methanol and collected viacentrifugation. The new capping ligand of choice can then be added andstirred for several hours and then isolated by precipitating andcollected via centrifugation.

To assemble the nanostructure, the temporary host, for example,carboxy-thiol modified PSBs can be mixed with the pyridine capped gainmedium nanoparticles in dichloromethane (DCM) and allowed to complex for12-36 hours. Binding of the nanoparticle to the temporary host can bemonitored by absorption spectroscopy of the solution. Upon attachment ofthe nanoparticle to the PSB, these can be mixed with Fmoc-protectedamino thiol linkers for 24 hours at 40° C. while agitating. The‘oriented’ nanoparticles can then be cleaved from the PSB resin by theaddition of 95% trifluoroacetic acid (TPA) in DCM for one hour at roomtemperature

To attach one output coupler nanoparticle to the ‘oriented’ nanoparticleprepared above, one equivalent of the amino-silane linker coated outputcoupler nanoparticles can be added and the system can be agitated for24-48 hours. Once complexed, the amine groups on the output couplernanoparticle can be coupled to the silyl carboxylic acid linker in thepresence of five equivalents of dicyclohexylcarbodiimide (DCCI) ordiisopropylcarbodiimide (DICI).

The resulting gain medium nanoparticle/output coupler nanoparticle paircan either be attached to a metal/metalloid oxide substrate or furtherself-assembled in solution. If a solution process may be desired, thenthe two-particle pair is precipitated from solution with methanol andcentrifuged to isolate. To attach a first tier of SiO₂-coated metalnanoparticles, piperidine in DCM can be added, and the system can beagitated overnight. Six equivalents of carboxylic acid functionalizedSiO₂-coated metal nanoparticles may then added to the gain mediumnanoparticle/output coupler nanoparticle pair intermediate with sixequivalents of either DCCI or DICI. The temperature is then raised from0 to 20° C. over 2-4 hours. The resultant one-tier nanostructure canthen be isolated by precipitation from methanol with centrifugation andthen dispersed in fresh dry DCM.

To attach the second tier of SiO₂-coated metal nanoparticles, eightequivalents of amine-functionalized SiO₂-coated metal nanoparticles areadded to the one tier nanostructure in the presence of eight equivalentsof either DCCI or DICI. The temperature is then raised from 0 to 20 C.over 2-4 hours. The final nanostructure assembly can then precipitatedwith methanol, centrifuged, and dispersed in minimal anhydrous DCM tothe required concentration. This solution can then be treated withexcess trichloroacetyl chloride if required. The fully assembled devicesolution may then be added dropwise to oxide supports and the solventcan be allowed to evaporate, resulting in the fully assemblednanostructure anchored to an oxide support.

FIGS. 6A and 6B depict exemplary processes that create a protectedsurface on a gain medium nanoparticle. As shown in FIG. 6A, a gainmedium nanoparticle 610 has binding sites capped with protecting groupelements 620 a to 620 d. There is also provided a linker 630 which hasterminal ends 650 and 660. Terminal end 660 is linked to a temporaryhost 640.

In an exemplary embodiment, in FIG. 6A, the gain medium nanoparticle 610has binding sites capped with pyridine 620 a through 620 d, though otherprotecting groups could be used to cap the binding sites. There isprovided an exemplary carboxylic acid thiol linker 630 which can attachto an exemplary polystyrene bead 640 at the carboxylic acid terminalgroup 650, although there may be other larger diameter substrates andother organic linkers used in other exemplary embodiments. As one of thepyridines 620 leaves, the thiol terminal group 660 of the attachedlinker can bind to the gain medium nanoparticle.

FIG. 6B shows a gain medium nanoparticle 610 with one of the protectinggroup elements 620 d removed. The gain medium nanoparticle is linked tothe linker 630 at the terminal end 660. Terminal end 650 attached to thetemporary host 640.

In an exemplary embodiment, FIG. 6B shows the removed pyridine group andthe gain medium nanoparticle 610 attached to the polysterene bead 640via the carboxylic acid thiol linker 630. The gain medium nanoparticleis then removed from the substrate by detaching the carboxylic acidthiol linker from the polystyrene bead. By removing the gain mediumnanoparticle from the polystyrene bead, an ‘active’ carboxylic acidterminal group can be exposed for connection to an amino silyl coatedoutput coupler nanoparticle in a further step of the assembly process.In another step, the capping pyridines can be replaced with exemplaryorganic linkers Fmoc-protected amino thiols. In some embodiments of thisinvention, these linkers could be other types of organic linkers whichhave protected terminal groups.

FIGS. 7A and 7B depict exemplary processes that attaching a gain mediumnanoparticle 710 to an output coupler nanoparticle 760. As shown in FIG.7A, a gain medium nanoparticle 710 may be surrounded by protecting groupelements 720 a to 720 c as well as a linker 730 which includes a firstterminal group element 740 that attaches to the gain medium nanoparticle710 and has another terminal group element 750. There is also shown anoutput coupler nanoparticle 760 which may be surrounded by linkers 775 ato 775 d. These linkers have first terminal elements 770 a to 770 d thatattach to the output coupler nanoparticle 760 and have second terminalelements 780 a to 780 d.

In an exemplary embodiment, FIG. 7A includes a gain medium nanoparticle710 surrounded by Fmoc-protected ammo thiols 720 a to 720 c and acarboxylic acid thiol linker 730 which attaches to the gain mediumnanoparticle to at a thiol (SH) group 740 and has an ‘active’ carboxylicacid (COOH) terminal group 750. FIG. 7A also shows an exemplary outputcoupler nanoparticle 760 surrounded by amino silyl linkers which attachto the output coupler nanoparticle 760 at a silane (SiH₄) functionalgroup 770 a to 770 d and has an amino (NH₃) terminal functional group780 a to 780 d, any one of which can bind to the carboxylic acidterminal group 750.

In FIG. 7B the gain medium nanoparticle and the output couplernanoparticle are able to be linked together at a connection point 790.In an exemplary embodiment, FIG. 7B shows the nitrogen of the aminogroup 780 b, for example, and the doubly bonded oxygen of the carboxylicacid group 750 having rearranged to form an amide group 790, effectivelyconnecting the gain medium nanoparticle 710 and the output couplernanoparticle 750. This can permit the linkers to connect by peptidebonding, similar to the bonding mechanism of amino acids, where theamine functional groups can, for example, bond to the carboxylic acidfunctional groups. After these two nanoparticles have been connected,the Fmoc protecting groups on the Fmoc-protected amino thiols 720 a to720 c may be removed to expose, an ‘active’ amine group for each ofthese linkers.

FIGS. 8A and 8B show the steps of assembling a tier of metalnanoparticles to surround a gain medium nanoparticle. For example, FIG.8A shows a gain medium nanoparticle 801 attached to an output couplernanoparticle at connection point 815. This connection is detailed abovein FIGS. 7A and 7B. FIG. 8A also shows the gain medium nanoparticle 810surrounded by linkers including a first terminal group 820 a to 820 cattached to the gain medium nanoparticle as well as a second terminalgroup 830 a to 830 c. There is also shown a metal nanoparticle 840surrounded by linkers that include a first terminal group 850 a to 850 cand a second terminal group 860 a to 860 c. Any one of the terminalgroups 830 a to 830 c has the ability to connect to any one of theterminal groups 860 a to 860 c. In FIG. 8B, a connection point 870 isshown which connects the gain medium nanoparticle 810 to the metalnanoparticle 840.

In an exemplary embodiment, in FIG. 8A, a gain medium nanoparticle 810is surrounded by amino thiol linkers, which attach to the gain mediumnanoparticle 810 at thiol groups 820 a to 820 c. These linkers haveamino (NH₃) terminal groups 830 a to 830 c. FIG. 8A also shows exemplarymetal nanoparticle 840 surrounded by carboxy silyl linkers which attachto the metal nanoparticle at silane (SiH₄) functional groups 850 a to850 d and has carboxylic acid (COOH) terminal functional groups 860 a to860 d, any one of which will preferably bind to any one of the aminogroups 830 a to 830 c. This is shown in FIG. 8B where the gain mediumnanoparticle 810 and the metal nanoparticle where the nitrogen of theamino group 830 b, for example, and the doubly bonded oxygen of thecarboxylic acid group 860 b, for example, have rearranged to form anamide group 870, effectively connecting the gain medium nanoparticle 810and the metal nanoparticle 840 via a peptide bond.

Injection into the nanostructure can be achieved through chargeconducting organic linker ligands. These linkers can act as molecular“wires,” linking the nanostructure to the electrodes of an exemplaryinjection structure and serving as charge-transfer linkers for theexcitons. These wires work by tunneling electrons in and out of thenanostructure, thus providing carriers and current FIG. 9 shows thenanostructure 910 bonded to metal electrodes 930 a and 930 b via chargeconducting linkers 940 a and 940 b. Light impinging on the gain mediumnanoparticle will generate electron-hole pairs (excitons) which can betransported through the charge-conducting linkers, enabling current toflow. The electrodes 930 a and 930 b may comprise, for example, indiumtin oxide (ITO), or another transparent conductive oxide such as zincdirhodium tetraoxide (ZnR₂O₄), niobium dioxyfluoride (NbO₂F) ormonoclinic gallium oxide (β-GaO₃) or other transparent metals. Electrodematerial also may comprise one or more thin metal layers such asaluminum (Al), copper (Cu), titanium (Ti), etc. Injection into thenanostructure can be accomplished by using charge conducting linkers 940a and 940 b. The conductive linkers may comprise organic chargeconducting linker material such as phenylacetylene, polyaniline,polypyrrole and the like, for example, or other suitable materials, allof which may be synthesized according to known methods.

Final attachment to an optically transparent surface can be carried outby using unused linkers on the surface of the output couplernanoparticle after at least one tier of metal nanoparticles has beenadded to the nanostructure. This can serve to provide orientation andanchoring for the nanostructure to an exemplary substrate or housingmedium. For example, thermal oxide can bind to the output couplernanoparticle to serve as a substrate for the nanostructure.

FIG. 10 shows an exemplary nanostructure with a gain medium nanoparticle1010 and one tier of metal nanoparticles 1020 a through 1020 c arrangedaround the gain medium nanoparticle 1010 connected with a first kind oflinker 1015 a through 1015 c, as well as an output coupler nanoparticle1030, with a second kind of linker 1035 connecting the nanostructure toan exemplary substrate 1040. This substrate may be thermal oxide or anyother substrate that will serve to anchor the nanostructure.

Because of the unique optical properties that can result from theinteractions between the gain medium and the feedback structure, and thethree-dimensional confinement these nanostructure assemblies are able toachieve, there is great potential for novel applications for thesestructures. Unlike a two-dimensional surface where a field can involve acertain polarization, where light entry can be limited to a certaindirection, and where the amount of field inside can depend strongly onthe direction (e.g., nanorods and nanowires that confine light only intwo dimensions), the three-dimensional (3-D) aspect disclosed herein issubstantially directionally independent. The 3-D structures describedherein can confine light propagating from almost any direction,resulting in a capacity for a greatly enhanced localized electric field.

For example, the enhanced electric field created by a super-structurearranged around some light-emitting nanoparticle such as a quantum dotor other gain, medium nanoparticle can be used to stimulate an increasein emission from that light-emitting nanoparticle. The 3-Dsuper-structure can alternatively be arranged around a non-linearmaterial, a magnetic material or even a molecule of heavy water, for thepurpose of confining light and focusing the electromagnetic energy fromall directions into localized spot. Additionally, while 3-D confinementis present in certain existing applications such as photonic band gapcrystals, these crystals can include many defects, and their growth andresulting form can be difficult to control. To generate enhancement, thecrystals are thousands of layers thick. As described herein, a means ofgenerating 3-D confinement can be achieved using several layers ofnanoparticles.

It will be apparent to those skilled in the art that various changes andmodifications can be made in the method and system for accumulating andpresenting device capability information of the present inventionwithout departing from the spirit and scope thereof. Thus, it isintended that the invention cover the modifications of this inventionprovided they come within the scope of the appended claims and theirequivalents.

What is claimed is:
 1. A method for assembling a nanostructure,comprising: attaching a first linker to a gain medium nanoparticle;attaching the first linker to a substrate larger than the gain mediumnanoparticle; attaching a plurality of second linkers to the gain mediumnanoparticle; detaching the first linker connected to the gain mediumnanoparticle from, the substrate; attaching a plurality of third linkersto an output coupler nanoparticle; attaching the first linker to one ofthe plurality of third linkers, such that the output couplernanoparticle is discrete from and linked to the gain mediumnanoparticle; attaching a plurality of fourth linkers to a plurality ofmetal nanoparticles; and attaching each of the plurality of secondlinkers to each of the plurality of fourth linkers, wherein the gainmedium nanoparticle and the output coupler nanoparticle are included inthe nanostructure in a one to one ratio.
 2. The method of claim 1wherein the first linkers are amino-silane ligands.
 3. The method ofclaim 1 wherein the second linkers are silyl-carboxylic acid ligands. 4.The method of claim 1 wherein the third linkers are carboxylicacid-thiol ligands.
 5. The method of claim 1 wherein the fourth linkersare FMOC-protected amino-thiol ligands.
 6. The method of claim 1,wherein the output coupler nanoparticle has a size ranging from about 10nanometers to about 350 nanometers.
 7. The method of claim 1, whereinthe output coupler nanoparticle and the gain medium nanoparticle arelinked together at a connection point.
 8. A nanostructure consisting of:one gain medium nanoparticle; a first linker attached to the gain mediumnanoparticle; a plurality of second linkers attached to the gain mediumnanoparticle; one output coupler nanoparticle; a plurality of thirdlinkers attached to the output coupler nanoparticle; a plurality ofmetal nanoparticles; and a plurality of fourth linkers, each of theplurality of fourth linkers being attached to one of the plurality ofmetal nanoparticles, wherein the first linker attaches to one of thethird linkers at a connection point such that the output couplernanoparticle is linked to the gain medium nanoparticle, wherein each ofthe second linkers such that the plurality of metal nanoparticles arelinked about the gain medium nanoparticle, and wherein the nanostructureis optionally attached to a substrate.